Recently, 80% or more of the capacities of some dams are filled with sand and gravels, thereby reducing dam operability and effectiveness.
To recover their function, an effective dredging method and an effective dredging apparatus are required.
Conventionally, sand and gravel deposites are removed by methods employing a dipper, a crab, a bucket, a pump or a siphon, which are selected according to the deposit condition of the sand and gravels.